1. Field of the Invention
The present invention relates to a multilayer ceramic substrate and a manufacturing method therefor, and more particularly, to a multilayer ceramic substrate including a resistance film therein and a manufacturing method therefor.
2. Description of the Related Art
For example, to measure the remaining battery power with a remaining-battery-power detection circuit, a current detection resistor with an ultralow resistance of 100 mΩ or less is necessary. Further, the current detection resistor is required to have a TCR (temperature coefficient of resistance), for example, of less than 100 ppm/° C.
For example, Japanese Unexamined Patent Application Publication No. 2004-356306 discloses a ceramic substrate equipped with a resistor that is formed by firing a resistor paste simultaneously with the ceramic substrate. For example, a resistor paste used in Japanese Unexamined Patent Application Publication No. 2004-356306 is mainly composed of ruthenium oxide. However, in the case of a ruthenium oxide resistor paste, an ultralow resistance of 100 mΩ or less cannot be realized with excellent TCR characteristics.
Further, when the substrate has a resistance film therein, conductor films are connected as lead electrodes to both ends of the resistance film, as in the technique described in Japanese Unexamined Patent Application Publication No. 2004-356306. In this case, however, if the area of connecting portions between the resistance film and the conductor films is large, alloying in the connecting portions is not negligible, and this affects the TCR characteristics. For this reason, even if a resistive material, for example, containing Ni and Cu is selected to achieve excellent TCR characteristics at a low resistance, the TCR characteristics are affected by alloying in the connection portions between the resistance film and the conductor films. This makes it difficult to obtain desired characteristics.
To solve the above problems, it is conceivable to lead out the resistance film by using via conductors. In this case, since the cross-sectional area of the via conductors is sufficiently smaller than the area of the resistance film, the area of connecting portions between the resistance film and the via conductors can be made smaller than the area of the above-described connecting portions between the resistance film and the conductor films. Hence, it is possible to reduce the influence on the TCR characteristics due to alloying in the connecting portions. For example, Japanese Unexamined Patent Application Publication No. 2009-147157 discloses a structure in which via conductors are connected to an internal wire contained in a multilayer ceramic substrate, and also discloses that a resistor is formed similarly to the internal wire.
However, when the structure in which the resistance film is led out by the via conductors with the emphasis on realization of excellent TCR characteristics, as described above, the area of the connecting portions becomes small. This causes a problem in that connection reliability between the resistance film and the via conductors decreases.